O B S E R V A T I O N S O F A I R C O M P O S I T I O N I N B R A Z I L B E T W E E N T H E E Q U A T O R A N D 20°S D U R I N G T H E D R Y S E A S O N .
P . J . C r u t z e n (*), M . T . C o f f e y (**), A . C . D e l a n y ( * * ) , J . G r e e n b e r g (**), P. H a a g e n s o n (**), L . H e i d t (**), R . L u e b (**), W . G . M a n k i n (**), W . P o l l o c k (**), W . S e i l l e r (*), A . W a r t b u r g P. Zinrnerman (**)
A B S T R A C T
Tizld mzaòunemznt pnognamò in Biazit duxing thz dh.y iza&on monthi Q& Auguit and
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tKopici, In globo? OÍA ch<míit>it<. Ei.pe.cA.atly in the. m-ixzd tayei, thz ÍUA comporcticn OMVlt tand ÍÁ much diÜ&fiQ.nt ^Kom thaX oi/ei thz octan and thz íand anzai OKZ ctzafiZy tange. &ca£z ÒOUICZÒ of, mamj in\poh£an£ txacz gaòzò. Vu-iing thz diu ÍZOÒOH much biomoa bu/iníng takeb ptacz zipzcialZu in thz czKKadv izgionò Izading to iubítantíat zrtüAbion oi ain. poUutantò, àuc/i ai CO, H0' f W^O, CH^ and othzn. hydKOQ.an.bonA. Ozonz conczntxat ícnò aiz aZ&oznhanczd due to photochzmicat izactiom. Siogznic oiganic zmiaionà f,A.om Viopical ^oKZAtò ptau likzuxuz an impoitant totz in thz photochemiòtAy oi thz atmoi-píiete. CaAbcn monoxidz totu JMÜtd to bz pnzbznt in high conczntH.ati.onA in thz boundaAU tay&l oí thz tAopicat hoiZAt, bat ozonz conczntAationi IMZAZ much touie.1 than in thz CZA hado.
(*) M a x - P l a n c k - I n s t i t u t f ü r C h e m i e , P o s t f a c h 3 0 6 0 , D 6 5 0 0 M a i n z , Germatiy
(**) N a t i o n a l C e n t e r f o r A t m o s p h e r i c R e s e a r c h , P.O. B o x 3 0 0 0 , B o u l d e r , C o l o r a d o 8 0 3 0 7 , U.S.A. (The N a t i o n a l C e n t e r f o r A t m o s p h e r i c R e s e a r c h is s p o n s o r e d b y the N a t i o n a l Science F o u n d a t i o n ) .
ACTA AMAZÔNICA, 1 5 ( 1 - 2) : 7 7 - l i g . 1985. 77 IWTRODUCTION
t i n e n t s . M o s t a v a i l a b l e i n f o r m a t i o n so f a r has b e e n g a t h e r e d d u r i n g the G A M E T A G a i r -c r a f t r e s e a r -c h f l i g h t s o v e r the P a -c i f i -c O -c e a n a n d w a s m o s t l y r e p o r t e d in the J o u r n a l o f G e o p h y s i c a l R e s e a r c h issue o f D e c e m b e r , 1 9 8 0 , w h i l e i m p o r t a n t a d d i t i o n a l i n f o r m a t i o n h a s a l s o b e e n g a t h e r e d by S e i l e r (197¾) a n d S e i l e r & F i s h m a n (1981) m o s t l y f r o m a i r c r a f t f l i g h t s a l o n g t h e c o a s t o f S o u t h A m e r i c a . E x c e p t for a f e w s t u d i e s c o n d u c t e d ' by F r e n c h r e s e a r c h w o r k e r s in the Ivory C o a s t ( M a r e n c o & O e l a u n a y , I 9 8 O ; D e l m a s « a l .
I 9 8 O } , s o m e e a r l v w o r k b v U . S . s c i e n t i s t s in t r o p i c a l P a n a m a a n d B r a z i l ( l o d g e & P a t e , 1 9 6 6 ; L o d g e e t a l . , 197¾) a n d s t u d i e s by B r i n k m a n n & d e S a n t o s (197¾) a n d S t a l l a r d & E d m o n d ( 1 9 8 1 ) , n o i n f o r m a t i o n is a v a i l a b l e o n the d i s t r i b u t i o n o f m o s t t r a c e g a s e s in the c o n t i n e n t a l , t r o p i c a l a t m o s p h e r e .
T h e m e a s u r e m e n t s w h i c h w i l l be r e p o r t e d in t h i s p a p e r a r e t h e r e f o r e u n i g u e in t h a t they p r o v i d e the f i r s t s u r v e y o f the d i s t r i b u t i o n o f t h e p h o t o c h e m i c a 1 l y a c t i v e t r a c e g a s e s 0 ^ , C O , h y d r o c a r b o n s a n d Ν 0χ in o n e o f the m o s t i m p o r t a n t r e g i o n s o f t h e c o n t i n e n t a l t r o p i c a l a t m o s p h e r e . T h e s e m e a s u r e m e n t s w e r e m a d e d u r i n g the m o n t h s o f A u g u s t a n d S e p t e m b e r , i.e., d u r i n g t h e d r y s e a s o n o v e r e q u a t o r i a l a n d s u b t r o p i c a l B r a z i l . B e s i d e s a i r c r a f t o b s e r v a t i o n s , a i r w a s a l s o s a m p l e d o n t h e g r o u n d for g a s chromato_ g r a p h i c d e t e r m i n a t i o n s o f s u c h a t m o s p h e r i c c o n s t i t u e n t s a s h y d r o c a r b o n s , n i t r o u s o x i d e a n d c a r b o n y l s u l f i d e .
T h e o b s e r v a t i o n s w h i c h will be r e p o r t e d in t h i s s t u d y a r e n o t o n l y i m p o r t a n t for o u r u n d e r s t a n d i n g o f g l o b a l a i r c h e m i s t r y in g e n e r a l , b u t a r e a d d i t i o n a l l y i m p o r t a n t b e c a u s e o f the l a r g e c h a n g e s w h i c h a r e t a k i n g p l a c e in t h e t r o p i c s in the a g r i c u l t u r a l s e c t o r . T h e d e f o r e s t a t i o n a c t i v i t i e s w h i c h a r e o c c u r r i n g in m a n y t r o p i c a l c o u n t r i e s h a v e b e e n m u c h d i s c u s s e d in the p r e s s a n d in s c i e n t i f i c c i r c l e s ( e . g . , N A S , 1 9 7 9 ) T h r o u g h t h e s e a c t i v i t i e s the c h e m i c a l c o m p o s i t i o n of the a i r is c h a n g i n g , n o t o n l y in t h e t r o p i c s , b u t a l s o w o r l d w i d e . Up to n o w t h e m o s t d e b a t e d issue h a s b e e n to w h a t d e g r e e the q l o b a l c a r b o n d i o x i d e b u r d e n o f t h e a t m o s p h e r e h a s b e e n i n f l u e n c e d by t r o p i c a l f o r e s t c u t t i n g ( e . g . , B o l l n e t a l . , 1 9 7 9 ; W o o d w e l l e t a l. , 1 9 7 8 ; S e i l e r & C r u t z e n , 1 9 8 0 ) . H o w e v e r , c a r b o n d i o x i d e p l a y s o n l y a m i n o r r o l e in the p h o t o c h e m i s -try o f the a t m o s p h e r e . L e s s a b u n d a n t g a s e s a r e far m o r e i m p o r t a n t . For i n s t a n c e , it has b e e n p r o p o s e d by Z i m m e r m a n e t a l. (1978) t h a t t r o p i c a l f o r e s t s a r e m a j o r p r o d u c e r s o f h y d r o c a r b o n g a s e s w h i c h a r e o x i d i z e d in t h e a t m o s p h e r e to c a r b o n m o n o x i d e ( C O ) . C O p l a y s a n i m p o r t a n t r o l e in the p h o t o c h e m i s t r y o f t h e global a t m o s p h e r e a s it is t h e m a i n c o n s t i t u e n t w i t h w h i c h the i m p o r t a n t h y d r o x y ! r a d i c a l r e a c t s in t h e t r o p o s p h e r e ( L e v y , 1 9 7 ) , 1 9 7 ¾ ; M c C o n n e l l e t a l . , 1 9 7 1 ) . T h e o r e t i c a l i n v e s t i g a t i o n s by C r u t z e n e t a l . , (1978) , C r u t z e n & fiidel (1983) a n d Vol ζ e t a l, (1981) h a v e i n d i c a t e d t h a t , m o s t l i k e l y , t h e r e is a large p r o d u c t i o n o f c a r b o n m o n o x i d e in the t r o p i c s a n d h y d r o c a r b o n o x i d a t i o n is p o s s i b l e s o u r c e . It w a s e a r l i e r s h o w n by C r u t z e n & F i s h m a n ( 1 9 7 7 ) t h a t m e t h a n e o x i d a t i o n a l o n e c a n n o t a c c o u n t for t h i s s o u r c e , so t h a t h i g h e r h y d r o c a r b o n g a s e s , e s p e c i a l l y i s o p r e n e , a n d the t e r p e n e s , c
1 oH
1 6 * m a y b e im Portant
T h e c o m p o s i t i o n o f t h e t r o p i c a l a n d t h e g l o b a l a t m o s p h e r e c a n a l s o b e i n f l u e n c e d ;by the b u r n i n g o f d e a d v e g e t a t i o n a n d w o o d d u r i n g t h e d r y s e a s o n in m a n y p a r t s o f t h e tropical w o r l d . T h i s is n o r m a l a g r i c u l t u r a l p r a c t i c e a n d is d o n e t o f r e e g r a s s l a n d s from d r y a n d u n p a l a t a b l e v e g e t a t i o n w i t h 1 i t t l e n u t r i t i o n a l v a l u e , t o g e t r i d o f weeds o r to c l e a r p r i m a r y o r s e c o n d a r y f o r e s t in o r d e r t o r a i s e c a t t l e o r t o g r o w a g r i cultural a n d o t h e r c a s h c r o p s f o r s o m e p e r i o d o f t i m e . T r a d i t i o n a l l y , in t h e f o r e s t s the land w a s l e f t t o r e g r o w , a l l o w i n g n u t r i e n t s g r a d u a l l y t o r e t u r n t o t h e s o i l . A f t e r a p e r i o d o f s e v e r a l d e c a d e s , t h i s s e c o n d a r y f o r e s t w a s c u t a g a i n a n d u s e d f o r a g r i c u l ture. T h i s a g r i c u l t u r a l f a r m i n g p r a c t i c e w h i c h g o e s u n d e r m a n y n a m e s , m o s t c o m m o n l y shifting a g r i c u l t u r e , sl<ash a n d b u r n c u l t i v a t i o n , f o r e s t f a r m i n g o r s w i d d e n c u l t i v a t i on, h a s b e e n p r a c t i c e d in t h e t r o p i c s f o r m a n y c e n t u r i e s , p e r h a p s m i l l e n i a a n d nay be considered a s t h e o I d e s t f o r m o f a g r i c u l t u r e . It w a s s t i l l c o m m o n p r a c t i c e in parts o f E u r o p e in t h e l a s t c e n t u r y . It w a s , o r in m a n y p a r t s o f t h e t r o p i c s s t i l l is the ma in c a u s e o f a i r p o l 1 u t i o n .
A n a l y s e s b y S e i l e r & C r u t z e n ( 1 9 8 0 ) a n d C r u t z e n e t a l . ( 1 9 7 9 ) h a v e s h o w n t h a t the b u r n i n g o f v e g e t a t i o n in t h e t r o p i c s c a n s u p p l y s u b s t a n t i a l a m o u n t s o f i m p o r t a n t trace g a s e s t o t h e a t m o s p h e r e , s u c h a s C O , N20 , N C ^ , C H ^ , C O S a n d C H ^ C l . In a l l c a ses the p o t e n t i a l s u p p l y o f t h e s e g a s e s t o t h e a t m o s p h e r e w a s f o u n d t o b e o f s i m i l a r magnitudes a s t h e i n d u s t r i a l i n p u t s .
W e c o n d u c t e d t w o e x p l o r a t o r y f i e l d p r o g r a m s in B r a z i l d u r i n g t h e d r y s e a s o n s o f 1979 a n d 1 9 8 0 . T h e p r o g r a m e m p l o y e d r e s e a r c h f l i g h t s u s i n g t h e N C A R t w i n e n g i n e S a b r e liner j e t a i r c r a f t , m o s t l y f o r c o n t i n u o u s , s i m u l t a n e o u s m e a s u r e m e n t s o f t h e m e t e o r o -gtcal p a r a m e t e r s , a n d t h e g a s e s 0 ^ , C O a n d Ν 0χ. A l s o , e v a c u a t e d c a n s w e r e f i l l e d with a i r in t h e a i r p l a n e o r o n t h e g r o u n d m a i n l y t o d e r i v e f u r t h e r i n f o r m a t i o n o n gaseous e m i s s i o n s f r o m b i o m a s s b u r n i n g . B r a z i l w a s c h o s e n f o r t h i s w o r k b e c a u s e o f i t s relative p r o x i m i t y t o o u r b a s e in t h e U . S . a n d b e c a u s e t h i s c o u n t r y c o m b i n e s b o t h extens fve f o r e s t s ( s e l v a ) a n d s a v a n n a - Ii k e ( c e r r a d o ) e c o s y s t e m s o n i t s t e r r i t o r y . In this p a p e r , w e r e p o r t r e s u l t s f r o m t h e f i r e e m i s s i o n s a m p l i n g p r o g r a m s a n d a i r c r a f t flights in 1 9 7 9 a n d 1 9 8 0 .
IMPORTANCE O F T H E T R A C E G A S E S S A M P L E D
T h e g a s e s C O , C H ^ a n d t h e o t h e r h y d r o c a r b o n s , N20 , N O ^ , 0^ a n d C O S a l l p l a y important r o l e s in a i r c h e m i s t r y a n d c l i m a t e . C a r b o n m o n o x i d e is t h e m a i n g a s w h i c h the h y d r o x y l r a d i c a l r e a c t s in t h e b a c k g r o u n d t r o p o s p h e r e , l e a d i n g t o t h e formation o f
coy
Rl C O + O H ⊅+ Η + C 02
g e n s u l f i d e , n i t r i c o x i d e a n d n i t r o g e n d i o x i d e ( L e v y , 1 9 7 1 , 1 9 7 ^ ; C r u t z e n e t a l I 9 7 8 ) . H y d r o x y l r a d i c a l s p l a y , t h e r e f o r e , a n e s s e n t i a l r o l e in t h e c y c l i n g o f many g a s e s t h r o u g h t h e a t m o s p h e r e . T h e y a r e f o r m e d t h r o u g h t h e p h o t o l y s i s o f o z o n e b y u l t r a v i o l e t s o l a r r a d i a t i o n b e l o w 3'9 n m , l e a d i n g t o t h e p r o d u c t i o n o f e l e c t r o n i c a l l y e x c i t e d a t o m i c o x y g e n :
R 2 0 + h v + 0 {' D) + 0- ( λ< 3 1 0 n m )
i I
f o l l o w e d b y t h e r e a c t i o n o f 0 ( D) w i t h w a t e r v a p o r
R 3 0 ( ' D) + H20 -+ 2 0 H
T h i s e x p l a i n s t h e l a r g e i m p o r t a n c e o f t r o p o s p h e r i c o z o n e in a i r c h e m i s t r y . O z o n e is , h o w e v e r , a l s o d e p l e t e d b y t h e s a m e a n d o t h e r r e a c t i o n s , s o t h a t r a t h e r l i t t l e o f it w o u l d b e p r e s e n t in t h e t r o p o s p h e r e , if a d d i t i o n a l r e a c t i o n s w o u l d n o t r e p l e n i s h the g a s in t h e t r o p o s p h e r e ( C r u t z e n & R i d e l , 1 9 8 3 ) . T h e o x i d e s o f n i t r o g e n (NO a n d N 02 ) p l a y a n i m p o r t a n t c a t a l y t i c r o l e in t h i s t r o p o s p h e r i c o z o n e p r o d u c t i o n ( C r u t z e n , I 9 8 3 ) , T h e s i m p l e s t s e t o f r e a c t i o n s l e a d i n g t o o z o n e f o r m a t i o n o c c u r s d u r i n g t h e o x i d a t i o n of C O
Rl C O + O H + Η P C 02
R*t Η 02 + Μ ⊅+ H 02 + Μ
R 5 H 02 4 N O -' O H + N 02
R 6 N 02 + h v + N O + 0 (> </»00nm)
R 7 0 + 02+ Μ -+ 0^ + Μ
n e t : C Ü + 2 02 + C 02 + 0^
L i k e w i s e , t h e o x i d a t i o n o f C H ^ m a y l e a d t o o z o n e f o r m a t i o n e . g . v i a
R 8 C H ^ + O H ^ C H3 + H20
R 9 C H3 + 02+ Μ * C H ^ + Μ
R I O C H 02 Ψ K & ⊅+ C H30 + N O ,
Rl 1 C H30 + 02 + C H20 + H 02
R 5 H 02 + N O + O H + N 0o
Rl 2 C H20 + h v y C O + H2 ( \ £ 3 5 0 n m )
R6 N 02 + h v + N O + 0 (2X)
R 7 0 + 02+ Μ + 03 + Μ (2X)
n e t : C H ^ + 4 02 -> C O + H2 + Η?0 + 2 0 ^
S i m i l a r r e a c t i o n p a t h s a r e f o l l o w e d d u r i n g t h e o x i d a t i o n o f o t h e r h y d r o c a r b o n s a n d e x p l a i η t h e f o r m a t I o n o f h i g h o z o n e 1 e v e Is i η u r b a n e nν I r o m e n t s d u r i n g p h o t o c h e m i c a l s m o g e p i s o d e s w h e n m u c h m o r e r e a c t i v e h y d r o c a r b o n s t h a n C H ^ a r e o x i d i z e d in a
m a t t e r o f h o u r s o r d a y s . H y d r o c a r b o n s a r e p r o d u c e d in t h e t r o p i c s b y n a t u r a l p r o c e s s e s
1979). In a d d i t i o n , N O is a l s o p r o d u c e d b y l i g h t n i n g a n d t h i s s o u r c e m a y b e o f particular i m p o r t a n c e in t h e c o n t i n e n t a l , h u m i d t r o p i c s . A l t h o u g h t h e o x i d a t i o n o f CO and C H ^ o c c u r s m u c h m o r e s l o w l y t h a n t h a t o f o t h e r o r g a n i c s , t h e s e c o m p o u n d s a r e o m n i p r e s e n t in t h e a t m o s p h e r e a t m u c h h i g h e r c o n c e n t r a t i o n s a n d t h e i r o x i d a t i o n in t h e atmosphere c a n g i v e r i s e t o s u b s t a n t i a l o z o n e p r o d u c t i o n in t h e p r e s e n c e o f s u f f i c i e n t c o n c e n t r a t i o n s o f N O . O n t h e o t h e r h a n d , if t h e v o l u m e m i x i n g r a t i o o f N O n e a r t h e surface is l e s s t h a n a b o u t 10 p p t v (l p p t v = 10 1 2 b y v o l u m e ) t h e o x i d a t i o n o f C O leads to o z o n e l o s s v i a t h e r e a c t i o n s e t :
Rl C O + 0 H ~ + Η + C 02
Kk Η + 02+ M - > H 02 + Μ Rl 3 H 02 + 03 t O H + 2 02
C O +
o
3* c o
2+ o
2T h e a t m o s p h e r i c d i s t r i b u t i o n a n d t h e s o u r c e s a n d s i n k s o f N O a n d NO., p l a y , there_ fore, i m p o r t a n t r o l e s in t h e p h o t o c h e m i s t r y o f t h e a t m o s p h e r e . I n c r e a s i n g c o n c e n t r a tions o f N O in t h e t r o p o s p h e r e w i l l l e a d t o m o r e o z o n e . W e w i l l s e e t h a t t h e o p p o s i t e Is true in t h e s t r a t o s p h e r e .
T h e o x i d e s o f n i t r o g e n N O a n d N 02 a r e r e m o v e d f r o m t h e t r o p o s p h e r e b y r e a c t i o n s with h y d r o x y l a n d o z o n e , l e a d i n g t o t h e f o r m a t i o n o f n i t r i c a c i d ,
Rl 3 N O + 0^ + N 02 + 02
RI*» N 02 + O H ( + M ) + H N 03 ( + M )
HNOJ is r e m o v e d f r o m t h e t r o p o s p h e r e in l e s s t h a n o n e w e e k b y r a i n f a l l . T h e m a i n s o u r ces of c a r b o n m o n o x i d e in t h e t r o p o s p h e r e a r e o x i d a t i o n o f h y d r o c a r b o n s , i n d u s t r i a l emissions a n d b i o m a s s b u r n i n g ( Z i m m e r m a n e t a l ., 1 9 7 8 ; S e i l e r , 1 9 71* ; C r u t z e n e t a l . 1979; L o g a n e t a l . , 1 9 8 1 ) . H y d r o c a r b o n s , c a r b o n m o n o x i d e , o z o n e a n d t h e n i t r o g e n oxides i n t e r a c t , t h e r e f o r e , ρ h o t o e h e m i c a l l y in i n t r i c a t e w a y s , w i t h t h e h y d r o x y 1 radical a c t i n g a s a n i m p o r t a n t l i n k . T h i s r a d i c a l is f o r m e d f r o m o z o n e p h o t o l y s i s , c a r bon m o n o x i d e is r e m o v e d b y r e a c t i o n w i t h O H , b u t it is f o r m e d a s a n i n t e r m e d i a t e in the o x i d a t i o n o f t h e h y d r o c a r b o n s w h i c h is i n i t i a t e d b y r e a c t i o n w i t h O H . O z o n e m a y be f o r m e d d u r i n g t h e o x i d a t i o n o f c a r b o n m o n o x i d e , m e t h a n e a n d o t h e r h y d r o c a r b o n s in the p r e s e n c e o f s u f f i c i e n t a m o u n t s o f n i t r i c o x i d e , o t h e r w i s e o z o n e m a y b e d e s t r o y e d .
N i t r o u s o x i d e ( N O ) a n d c a r b o n y l s u l f i d e ( C O S ) p l a y i m p o r t a n t r o l e s in s t r a t o s pheric p h o t o c h e m i s t r y . T h e o x i d a t i o n o f N20 b y r e a c t i o n w i t h t h e 0 ( D) a t o m
R15 0 (1 D) + N20 * 2 N 0
R13 N O + O - N 02 + 02 RI6 03 + h v * 0 + 02 R17 N O . + O + N O + O
* 2 n e t : Z 03 ⊅* 3 02
T h i s is t h e m a i n s e t o f r e a c t i o n s l i m i t i n g t h e a b u n d a n c e o f o z o n e in t h e stratos_ p h e r e ( C r u t z e n , 1970). S e v e r a l p r o c e s s e s lead to t h e p r o d u c t i o n o f n i t r o u s o x i d e a t the e a r t h ' s s u r f a c e : d e n i t r i f i c a t i o n a n d n i t r i f i c a t i o n p r o c e s s in w a t e r s a n d s o i l s ( C o n r a d & Sei l e r , 1 9 8 0 ; B r e m n e r e t a l . , 1981 ; El k i n s e t a l . , 1978) , coal , oi 1 a n d g a s c o m b u s t i o n (Pierotti a n d R a s m u s s e n , 1 9 7 6 ; W e i s s & C r a i g , 1976) a n d b i o m a s s b u r n i n g ( C r u t z e n e t a l . , 1 9 7 9 ) . N o i m p o r t a n t s i n k s o f N j O h a v e s o f a r b e e n i d e n t i f i e d
in t h e t r o s p o s p h e r e . In t h e s t r a t o s p h e r e N20 is m a i n l y r e m o v e d b y t h e a c t i o n o f u l t r a v i o l e t r a d i a t i o n w i t h r e a c t i o n R 1 5 c o n t r i b u t i n g a b o u t 10¾ o f t h e total r e m o v a l .
C a r b o n y l s u l f i d e (COS) is i m p o r t a n t b e c a u s e it is p r o b a b l y t h e m a i n p r e c u r s o r o f the a e r o s o l layer in t h e s t r a t o s p h e r e d u r i n g p e r i o d s w i t h low v o l c a n i c a c t i v i t y (Crut -z e n , I 9 7 6 ) . T h i s layer c o n s i s t s m a i n l y o f p a r t i c u l a t e s u l f a t e ( J u n g e e t a l . , I96I ) a n d is p r o b a b l y f o r m e d b y t h e o x i d a t i o n o f S 02, w h i c h in its turn is p r o d u c e d f r o m C O S b y a b s o r p t i o n o f u l t r a v i o l e t r a d i a t i o n a n d f o l l o w i n g r e a c t i o n s R19 a n d R 2 0 :
ftl8 C O S + h v · C O + S
R19 S + 0 ,
* so + 0
R20 SO + 02 * S 02 + 0
T h e s t r a t o s p h e r i c s u l f a t e a e r o s o l l a y e r p l a y s a r o l e in t h e e a r t h ' s r a d i a t i o n b a l a n c e b y r e f l e c t i n g a small f r a c t i o n o f t h e i n c o m i n g s o l a r r a d i a t i o n b a c k t o s p a c e
M E T E O R O L O G I C A L O V E R V I E N
T h e d r y s e a s o n in t h e e q u a t o r i a l a n d s u b t r o p i c a l r e g i o n s o f B r a z i l l a s t s f r o m I about J u n e t o O c t o b e r . D u r i n g t h i s p e r i o d a s t r o n g a n t i c y c l o n i c s u b s i d e n c e s t a b l e l a y
er o f t e n s u p p r e s s e s c o n v e c t i o n , e s p e c i a l l y In t h e s u b t r o p i c s , t h e r e b y l i m i t i n g rainfall a n d t h e u p w a r d t r a n s f e r o f g a s e s a n d p a r t i c u l a t e s f r o m t h e b o u n d a r y l a y e r During t h i s t i m e p e r i o d e x t e n s i v e b i ' o m a s s b u r n i n g t a k e s p l a c e , s o t h a t h i g h c o n c e n t r a -I tions o f g a s e o u s a n d p a r t i c u l a t e e f f l u e n t s f r o m t h e f i r e s c a n a c c u m u l a t e in t h e l o w e s t I 2-3 K m o f t h e a t m o s p h e r e . M e t e o r o l o g i c a l d a t a f r o m B r a z i l a r e a v a i l a b l e f r o m t h e
I c o l l e c t i o n s o f t h e N a t i o n a l M e t e o r o l o g i c a l C e n t e r , N M C ) o f t h e U . S . A d d i t i o n a l m e t e o r o logical i n f o r m a t i o n w a s o b t a i n e d o n b o a r d o f t h e r e s e a r c h a i r c r a f t . A t h o r o u g h c l i m a -tological s t u d y o f t h e m e t e o r o l o g y o f t h e A m a z o n r e g i o n h a s b e e n p r e s e n t e d b y K o u s k y & ⊅ .Kagano ( 1 9 8 1 ) .
H e r e w e d e s c r i b e t h e c i r c u l a t i o n p a t t e r n s a n d t h e v e r t i c a l s t a b i l i t y o f t h e a t m o s p h e r e o v e r B r a z i l f o r s o m e a r b i t r a r i l y s e l e c t e d d a t e s d u r i n g t h e e x p e d i t i o n o f I Ί 9 8 Ο . H e i g h t c o n t o u r s a n d o b s e r v e d w i n d s f o r A u g u s t 28, a n d A u g u s t 3 1 , 1 9 8 0 f o r t h e
500 m b a n d 8 5 O m b p r e s s u r e l e v e l s r e s p e c t i v e l y a r e p r e s e n t e d in F i g u r e s 1 a n d 2 . H o r l -zontal p l o t s a r e c o n t o u r e d f r o m a n o c t a g o n a l g r i d d a t a a r r a y p r o v i d e d b y N M C o n a S o u t h Polar s t e r e o q r a p h i c m a p p r o j e c t i o n . T h e 8 5 O m b p r e s s u r e l e v e l m a y g e n e r a l l y b e c o n s i d e red to r e p r e s e n t m e a n c o n d i t i o n s in t h e b o u d a r y l a y e r w h i c h u s u a l l y e x t e n d e d u p t o about 7 5 0 m b (= 2. 5 K m ) f o r m o s t o f t h e a r e a o f i n t e r e s t . T h e t o p o f t h e b o u n d a r y l a y er o v e r t h e t r o p i c a l f o r e s t s i s o f t e n d i f f i c u l t t o d e f i n e f r o m t h e m e t e o r o g o g í c a l d a t a Its l o c a t i o n w a s , h o w e v e r , m u c h m o r e e a s i l y d e f i n a b l e o n t h e b a s i s o f t h e c h e m i c a l o b s e r v a t i o n s , e s p e c i a l l y t h o s e o f w a t e r v a p o r a n d c a r b o n m o n o x i d e . T h e a v e r a g e f l o w p a t t e r n s f o r t h e m o n t h o f A u g u s t a r e d e p i c t e d in F i g u r e s 3 a n d k, w h i c h s h o w t h a t t h e p r e v a i l i n g c o n d i t i o n s o n t h e d a y s o f A u g u s t 2 8 a n d 3 1 , I 9 8 O , a s d e p i c t e d in F i g s . 1 and 2 , d i d n o t d i f f e r a p p r e c i a b l y f r o m t h e m e a n . T h e s a m e w a s t r u e d u r i n g 1 9 7 9 . T h e s e d i a g r a m s s h o w t h a t d u r i n g t h e d r y s e a s o n , t r o p i c a l B r a z i l , n o r t h o f 1 0 ° S , e x p e r i e n -ces e a s t e r l y f l o w u p t o m i d - t r o p o s p h e r i c l e v e l s w h i l e s u b t r o p i c a l B r a z i l is m o r e f r e q u e n t l y s u b j e c t t o m i d l a t i t u d e c i r c u l a t i o n p a t t e r n s . T h e m e a n r e s u l t a n t w i n d d i r e c -t i o n i n -t h e b o u n d a r y l a y e r o v e r S o u -t h A m e r i c a in A u g u s -t is g i v e n in F i g u r e ^ - A n -t i c y c l o n i c c i r c u l a t i o n a s s o c i a t e d w i t h t h e s u b t r o p i c a l h i g h p r e s s u r e c e l l s r e s u 1 t s in e a s i e r I y t r a d e winds t h r o u g h o u t t h e b o u n d a r y l a y e r o v e r m u c h o f B r a z i l . A s i g n i f i c a n t c o n s e q u e n c e of the b o u n d a r y l a y e r f l o w c o u p l e d w i t h t h e u p p e r l e v e l c i r c u l a t i o n Is a s y s t e m a t i c d e c r e a s e , p o l e w a r d f r o m t h e e q u a t o r , in t h e v e r t i c a l e x t e n t o f t h e e a s t e r l i e s .
f e a t u r e w h i c h is i n t e r r u p t e d o n l y o c c a s i o n a l l y b y t h e n o r t h w a r d e x t e n s i o n o f m ΐ d — 1 a t i tu d e s y n o p t i c d i s t u r b a n c e s . In t h e A m a z o n B a s ΐ η o f t r o p í c a I Β r a z i1 , h o w e v e r , s u c h s t a -b l e c o n d i t i o n s a r e l e s s p r o n o u n c e d a n d c o n v e c t i v e a c t i v i t y o c c u r s m o r e f r e q u e n t l y . This f a c t a n d t h e s h o r t e r t r a n s i t t i m e f r o m t h e o c e a n i c w a t e r v a p o r s o u r c e e x p l a i n the s m a l l e r d e w p o i n t d e p r e s s i o n s a b o v e t h e b o u n d a r y l a y e r w h i c h w e r e o b s e r v e d t h e r e c o m -p a r e d t o o v e r s u b t r o -p i c a 1 B r a z i1. D u r i n g 1 9 8 0 t h e a n t i - e y e 1 o n i c c i r c u 1 a t i o n o v e r Β r a z ΐ 1 w a s s o d o m i n a n t t h a t m i d - l a t i t u d e s y n o p t i c d i s t u r b a n c e s c o u l d n o t p e n e t r a t e t o s u b t r o p | c a t B r a z i l . In 1 5 7 9 m o r e f r e q u e n t o c c u r r e n c e o f r a i n f a l l o c u r r e d in t h e B r a s i l i a re gi o n , s o m e t i m e s l e a d i n q t o p o s t p o n e m e n t s o f b u r n i n g a c t i v i t i e s a n d h a m p e r i n g o u r s a m -ρ 1 Ϊ n q p r o g r a m .
E X P E R I M E N T A L E Q U I P M E N T A N D F L I G H T P A T H S
T h e N C A R t w i n - e n g i n e S a b r e l i n e r j e t a i r c r a f t w a s i n s t r u m e n t e d t o d e t e r m i n e the c o n c e n t r a t i o n o f 0 ^ , C O , N O a n d N O X , a s w e l l a s r e l a t i v e h u m i d i t y , t e m p e r a t u r e , a i d t u d e , p o s i t i o n , w i n d s p e e d a n d d i r e c t i o n a n d t o c o l l e c t a m b i e n t a i r s a m p l e s f o r s u b s e q u e n t a n a l y s i s o f s t a b l e g a s e s .
O z o n e w a s m e a s u r e d u s i n g a D a s i b i 1 0 0 8 A H u l t r a v i o l e t a b s o r p t i o n i n s t r u m e n t ( 0 a s i b i , 1 9 7 9 ) s a m p l i n g f r o m a n i n t a k e v i a t h e a i r c r a f t e n v i r o n m e n t a l a i r s y s t e m . This s y s t e m w a s f o u n d t o b e s o m e w h a t c o m p r o m i s e d d u r i n g f u l l t h r o t t l e a s c e n t s a n d s o o z o n e v a l u e s m e a s u r e d d u r i n g a s c e n t w e r e l a t e r d i s c a r d e d . W e a r e a w a r e o f t h e s t u d y by H u n t z i c k e r S J o h n s o n ( 1 9 7 9 ) w h o f o u n d a n i n t e r f e r e n c e in t h e m e a s u r e m e n t s o f o z o n e by t h e D a s i b i I n f o r e s t f i r e p l u m e s . A l l o z o n e d a t a w h i c h w i l l b e r e p o r t e d in t h i s p a p e r a r e , h o w e v e r , o b t a i n e d o u t s i d e pi u m e s , s o t h a t t h e 1 i k e 1 I h o o d o f i i n t e r f e r e n c e is si i m .
D u r i n g t h e 1 9 7 9 m e a s u r e m e n t p r o g r a m , C O w a s m e a s u r e d b y a n i n f r a r e d s p e c t r o s c o p i c m e t h o d w h i c h u t i l i z e d a h i g h r e s o l u t i o n F o u r i e r t r a n s f o r m s p e c t r o m e t e r ( M a n k i n , 1 9 7 8 ) , a n d a l o n g p a t h a b s o r p t i o n c e l l ( M a n k i n & C o f f e y , 1 9 7 9 ) c o n t a i n i n g the a t m o s p h e r i c s a m p l e t o b e a n a l y z e d . T h e a p o d i z e d s p e c t r a l r e s o l u t i o n w a s 0 . 0 6 c m '. For m e a s u r e m e n t s o f C O , t h e r e g i o n f r o m 2 1 5 0 t o 2 ΐ 8 0 c m 1 w a s u s e d , e n c o m p a s s i n g t h e R (I) t h r o u g h R ( 9 ) l i n e s o f t h e p r i n c i p a l i s o t o p e . T y p i c a l s m o k e p l u m e s p e c t r a are s h o w n in F i g . 7 . T h e s y s t e m is d e s i g n e d t o h a v e a s h o r t r e p o n s e t i m e (^ 1 0 S) to c h a n g e s in C O a m o u n t s o t h a t t h e s t r u c t u r e o f s m o k e p l u m e s c o u l d b e d e t e r m i n e d from t h e f a s t m o v i n g a i r c r a f t .
D u r i n g t h e 1 9 8 0 c a m p a i g n c a r b o n m o n o x i d e w a s m e a s u r e d w i t h a n i n s t r u m e n t b a s e d o n t h e H g O - H g c o n v e r s i o n a n d d e t e c t i o n o f H g ( S e i l e r , e t a l ,1 9 8 0 ) . T h i s i n s t r u m e n t s h a r e d t h e s a m e I n t a k e a s t h e o z o n e s y s t e m , b u t b e c a u s e o f t h e g r e a t e r s t a b i l i t y of C O t h e r e w a s n o p r o b l e m d u r i n g a s c e n t s a n d s o t h e f u l l d a t a s e t c o u l d b e u t i l i z e d .
while the other utilized a hot molydenum converter at 375° and measured NOX, the sum
of most odd nitrogen compounds. A considerable {= 0.75 ppbv) NO signal was observed
for these instruments which was possibly the effect of hydrocarbon interference. This
rendered the clean air data suspect and NOX values have been utilized only for the
cerrado boudary layer portions of the mission. Here the elevated (up to 10 ppbv) con
centration of NOX tend to decrease the effect of the high background reading.
Data provided by these continuous instruments were displayed on chart recorders
and recorded along with relative humidity, temperature, pressure, inertial navigation
arid aircraft attitude inputs on magnetic tape for subsequent computer analysis.
The aircraft was also fitted with sampling manifolds which allowed evacuated
stainless steel cans to be filled with ambient air. These aircraft samples, together
with ground samples, were analyzed for stable gases such as C 02 , Ν,,Ο, COS, C H ^ and
many other hydrocarbons. Analyses of samples were in many cases conducted within a
few days in our temporary laboratories in Brazil. Many samples were also taken back
to NCAR in Boulder for further analysis The hydrocarbon analyses from the 1979
work were all completed at NCAR. In 1979, when most of our efforts were devoted to
biomass burning emissions in the cerrado regions of Central Brazil, a laboratory was
set up in the Physics Deapartment of the University of Brasilia. In 1980, the equip
-merit, including instruments for hydrocarbon analysis, was installed at INPA, in Mana
us. Besides the aircraft air samples, many evacuated cans were filled on the ground ,
mostly to determine the production of effluents from biomass burning. A few cans were
also filled above the clean forest canopy to obtain some information on the background
concentration of the afore-mentioned gases. These samples provided some first informa
tlon on the distribution of gases in the clean environments of the tropical forests.The
sampling and measurement techniques for CO^, C H ^ , C O , Ν,,Ο and COS have been previously
described by Heidt (1978). All hydrocarbon analyses were performed on aHewlett-Packard
5 8 8 0
gas chromatograph equipped with flame ionization detectors.
The aircraft research flights and the ground sampling sites are displayed in
Figure 8 . In 1979 most of the ground sampling was in the Brasília-Cuiaba region, where
as in
I 9 8 Omost ground sampling was in the Manaus region. The two most important
ecosystems of Brazil are the tropical forests (selva) and the cerrado, which is a
savanna-type vegetation mostly covered with grasses and scattered trees at most 10 rrt
high. In the cerrado, extensive burning takes place during the dry season, mostly of
grass and shrubs. This involves . 1arge areas. On limited size plots, burning takes
place also in the forest areas to open new land for agriculture. The area which was
most affected by land clearing was located in Mato Grosso near Cuiabá.
F i g u r e 8. O n e f l i g h t w a s a l s o d e v o t e d t o d e t e r m i n i n g t h e v e r t i c a l d i s t r i b u t i o n o f CO in c o n d i t i o n s f r e e f r o m s m o k e . T h e f l i g h t f o r m a t w a s t o d e s c e n d f r o m a h i g h a l t i t u d e (^ 12 K m ) a n d p e r f o r m s t n a i g h t a n d l e v e l f l i g h t s a t a n u m b e r o f a l t i t u d e s o v e r t h e same l o c a t i o n ( d e n o t e d D o n F i g u r e 8 ) .
D u r i n g t h e 1 9 8 0 a i r c r a f t f l i g h t s , e m p h a s i s w a s o n a r e a s f r e e o f s m o k e p l u m e s , F l i g h t s 7 , 8 a n d 9 , d e p i c t e d in F i g u r e 8 , w e r e f l o w n t o t h e n o r t h e a s t o f M a n a u s in a n o n - d e v e l o p e d a r e a . F l i g h t s 1 0 , 1 1 , 12 a n d 1 3 m a d e a n e x c u r s i o n s o u t h i n t o the c e r r a d o . D u r i n g t h e l o w a l t i t u d e p o r t i o n s o f t h e s e f l i g h t s , c a r e w a s t a k e n t o a v o i d t h e p l u m e s f r o m t h e l a r g e a n d n u m e r o u s f i r e s , a l t h o u g h , o f c o u r s e , t h e e n t i r e b o u n d a r y l a y e r w a s f i l l e d w i t h p o l l u t e d a i r . F l i g h t s 1^ a n d 1 5 w e r e m a d e s p e c i f i c a l l y to i n v e s t i g a t e f i r e s a s s o c i a t e d w i t h t h e j u n g l e c l e a r i n g t o t h e s o u t h w e s t o f M a n a u s .
F l i g h t 16 w a s m a d e t o t h e w e s t o f M a n a u s , a n d a s e r i e s o f l o w l e v e l t r a n s i t s w e r e m a d e o v e r a r e g i o n o f u n p e r t u r b e d j u n g l e .
A t y p i c a l f l i g h t p r o f i l e f o r t h e 1 9 8 0 f l i g h t s is s h o w n in F i g u r e 11 s h o w i n g 6 v e r t i c a l p r o f i l e s f o r m t h e l o w e r b o u n d a r y l a y e r t o a l i t t l e o v e r 10 K m . A l t o g e t h e r ^ 5 0 v e r t i c a l p r o f i l e s w e r e o b t a i n e d , a b o u t 2 0 o v e r t h e c l e a r j u n g l e , 1 5 o v e r t h e c e r -r a d o w i t h a f u -r t h e -r 1 5 e i t h e r i n t h e t r a n s i t i o n a r e a o r i n t o f i r e s m o k e .
B e c a u s e s o m e o f t h e i n s t r u m e n t s w e r e o p e r a t e d a t c a b i n p r e s s u r e , it w a s the p r a c t i c e t o h o l d p r e s s u r e c o n s t a n t a t 1 a t m o s p h e r e w h e n t h e a i r c r a f t o p e r a t e d a t or b e l o w 6 K m a n d t o c h a n g e t o a c o n s t a n t 0.8 a t m o s p h e r e w h e n t h e a i r c r a f t o p e r a t e d a b o v e t h i s a l t i t u d e . T h i s p r a c t i c e a c c o u n t s f o r t h e s t e p - l i k e c h a r a c t e r o f t h e f l i g h t p r o f i l e s .
R E S U L T S O F B I O M A S S B U R N I N G E X P E R I M E N T S A N D B A C K G R O U N D S A M P L E S
physical a n d c h e m i c a l f a c t o r s w h i c h i n f l u e n c e t h e e m i s s i o n r a t e r a t i o s r e m a i n s a n i m p o £ tant t a s k in t h e f u t u r e .
T h e e m i s s i o n r a t e r a t i o s o b t a i n e d f r o m t h e f i r e s a m p l e s in B r a z i l a r e p r e s e n t e d in T a b l e 1 . T h e a v e r a g e e m i s 5 i o n r a t i o s w h i c h w e r e p u b 1i s h e d in t h e e a r l i e r s t u d y , based o n a m u c h m o r e l i m i t e d d a t a b a s e ( C r u t z e n e t a l . , 1 9 7 9 ) , a g r e e q u i t e w e l l f o r most g a s e s w i t h t h e e x c e p t i o n o f N ^ O . T h e d i f f e r e n c e in N ^ O y i e l d s b y a n o r d e r o f m a g n i t u d e is d u e t o a n e a r l i e r i n t e r f e r e n c e o f t h e N ^ O c h r o m a t o g r a p h i c p e a k b y C O ^ . 't
is c l e a r t h a t t h e r e i s a w i d e r a n g e o f p o s s i b l e e m i s s i o n r a t i o s w h i c h s t i l l s n e e d s t o be n a r r o w e d d o w n b y m o r e e x t e n s i v e a n d s y s t e m a t i c r e s e a r c h . T h e e m i s s i o n r a t i o s o f C O , Ch1
^ d e t e r m i n e d f r o m t h e c a n n i s t e r s s a m p l e d d u r i n g t h e a i r c r a f t s m o k e p l u m e f l i g h t s a r e also p r e s e n t e d in T a b l e 1. T h e a g r e e m e n t b e t w e e n t h e r a t i o s d e r i v e d b y g r o u n d a n d aircraft s a m p l Ϊ n g is e n c o u r a g i n g .
D u r i n g t h e B r a z i l e x p e r i m e n t s o f 1 9 7 9 a n d 1 9 8 0 , d e t e r m i n a t i o n s w e r e a l s o m a d e of n o n - m e t h a n e h y d r o c a r b o n e m i s s i o n s b y f i r e s a n d t h e d a t a a r e 1 i k e w i s e 1 i s t e d in T a ble 1. W e n o t i c e t h a t a l k e n e s c o n s t i t u t e a b o u t hS% o f t h e e m i s s i o n s , . w i t h e t h y l e n e t h e most i m p o r t a n t C o n t i b u t o r . N e x t in m a g n i t u d e (~2<t-%) a r e t h e e m i s s i o n s o f a l k a n e s , w i t h ethane a n d p r o p a n e a s t h e m o s t i m p o r t a n t g a s e s . E s p e c i a l l y t h e a l k e n e s a r e p h o t o c h e m i -cally r e a c t i v e in t h e t r o p o s p h e r e a n d t h e i r o x i d a t i o n m a y l e a d t o t h e f o r m a t i o n o f o z o ne, if s u f f i c i e n t N O is p r e s e n t in t h e a t m o s p h e r e . T h i s is l i k e l y in t h e c e r r a d o r e -gion s i n c e N O is p r o d u c e d b u r n i n g ( C l e m e n t s & M c M a h o n , 19 8 0) . It m a y b e m e n t i o n e d t h a t our CO a n d h y d r o c a r b o n e m i s s i o n f a c t o r s d o n o t d e v i a t e s u b s t a n t i a l l y f r o m e a r l i e r d e t e r ruinations ( s e e T a b l e 2 ) .
S o m e b a c k g r o u n d a i r s a m p l e s o f n a t u r a l a t m o s p h e r i c c o n s t i t u e n t s a r e i n t e r e s t i n g because t h e y w e r e g a t h e r e d a t l o w a l t i t u d e s o v e r t h e t r o p i c a l f o r e s t . O n e s e t o f s a m -pies w a s t a k e n a t n i g h t o n t o p o f a n a p p r o x i m a t e l y ^ 0 m e t e r h i g h m e t e o r o l o g i c a l t o w e r about 80 K m n o r t h o f M a n a u s ( u n f o r t u n a t e l y , a d a y t i m e s a m p l e w a s c o n t a m i n a t e d ) a n d another s e t o f d a t a w a s o b t a i n e d d u r i n g f l i g h t s b e t w e e n 3 0 a n d 3 6 0 m e t e r a l t i t u d e a b o v e the f o r e s t c a n o p y . T h e d a t a a r e s h o w n in T a b l e 3 . A l l v a l u e s a r e e x p r e s s e d a s c a r b o n atom v o l u m e m i x i n g r a t i o s , w h i c h m e a n s t h a t e . g . , f o r & έ % , t h e a v e r a g e v o l u m e mixing r a t i o Is o b t a i n e d b y d i v i d i n g t h e v a l u e in T a b l e 3 b y 5 T a b l e 3 i n d i c a t e s t h a t average d a y t i m e v o l u m e m i x i n g r a t i o o f i s o p r e n e f r o m 5 d a t a p o i n t s u p t o 3 60 m a l t i t u d e is equal t o 1.7 p p b v ( 1 . 7 x 10 ^ ) . D u r i n g t h e n i g h t t h e m e a s u r e d , a v e r a g e h y d r o c a r b o n mixing r a t i o a t c a n o p y h e i g h t is l o w e r t h a n d u r i n g t h e d a y . I s o p r e n e v a l u e s h a v e d r o p -.ped o n t h e a v e r a g e t o 0 . 9 p p b v . T h i s is in a c c o r d a n c e w i t h o b s e r v a t i o n b y S a n a d z e 1 9 6 3
who f o u n d i s o p r e n e e m i s s i o n r a t e s t o b e l i g h t d e p e n d e n t w i t h n o a p p r e c i a b l e e m i s s i o n s occurlng a t n i g h t .
RESULTS O F A I R C R A F T F L I G H T S
t h e l o c a l c o n c e n t r a t i o n s o f C O in s m o k e p l u m e s . S h o w n in t h e f i g u r e s a r e s c h e m a t i c re
p r e s e n t a t i o n s o f t h e s m o k e p l u m e s a n d t h e a i r c r a f t p a s s e s t h r o u g h t h e p l u m e s . T h e bar
g r a p h s s h o w c r o s s s e c t i o n s o f t h e l o c a l c o n c e n t r a t i o n s o f C O . E a c h b a r r e p r e s e n t s
a p p r o x i m a t e l y 10 s o f m e a s u r e m e n t . T h e p l u m e in F i g u r e 9 w a s in r e l a t i v e l y s t i l l air
a n d w a s n e a r l y v e r t i c a l . T h e p l u m e t e r m i n a t e d in a c l o u d d e c k a b o v e w h i c h n o smoke
w a s v i s i b l e . P a s s e s w e r e m a d e a b o v e t h e c l o u d a n d a t v a r i o u s a l t i t u d e s t h r o u g h the
s m o k e p l u m e . T h e p l u m e in F i g u r e 10 e x h i b i t e d a f a i r l y c o h e r e n t s h a p e b u t w a s d e f i n i
t e l y t i l t e d b y t h e w i n d .
A s m a y b e s e e n in F i g u r e s 9 a n d 1 0 , l a r g e c o n c e n t r a t i o n s o f C O (up t o 2 p p m v )
m a y b e f o u n d in t h e p l u m e s . T h e e f f e c t o f t h e l a r g e s c a l e b u r n i n g o n C O a m o u n t s in the
pi u m e f r e e , w e 1 Im i x e d , c e r r a d o b o u n d a ry 1 a y e r w a s t o i n c r e a s e g e n e r a 1 1 y t h e c o n c e n
-t r a -t i o n -t o 1 5 0 - 2 0 0 p p b v . I-t m a y b e s e e n , h o w e v e r , f r o m p a s s n u m b e r 1 a b o v e -t h e c l o u d
d e c k in F i g u r e 9 t h a t s o m e r e l a t i v e l y c l e a n a i r 9 0 p p b v ) h a d o v e r r i d d e n t h e CO
e n r i c h e d l a y e r b e l o w t h e c l o u d .
T h e r e s u l t s w h i c h w e r e o b t a i n e d o n t h e 1 9 8 0 a i r c r a f t f l i g h t s c a n b e d i v i d e d up
i η t o t h e f o l 1 o w i n g t h r e e c h a r a c t e r i s t i c r e g i o n s : 1) t h e b o u n d a r y 1 a y e r a b o v e t h e tropl
c a l f o r e s t , n o r t h o f a b o u t 6 ° S ; 2 ) t h e b o u n d a r y l a y e r a b o v e t h e c e r r a d o , s o u t h of
9° S ; 3 ) t h e f r e e t r o p o s p h e r e a b o v e t h e b o u n d a r y l a y e r .
T h e t o p o f m i x e d l a y e r w a s t y p i c a l l y l o c a t e d a t a b o u t 7 5 0 m b ( 2 . 5 K m ) in the
c e r r a d o a n d in t h e m e a n n e a r 8 0 0 m b (~2 K m ) a b o v e t h e f o r e s t s . T h i s c a n b e m o s t c l e a r
ly i d e n t i f i e d p a r t i c u l a r l y in t h e s u b - t r o p i c a l r e g i o n by t h e d e w p o i n t d e p r e s s i o n c u r v e s
( F i g s . 5 a n d 6 ) a n d in t h e r e l a t i v e h u m i d i t y p r o f i l e s o f F i g u r e s 12 a n d 1 3 a s t h e t r a n
s i t i o n s t e p t o a d e e p l a y e r o f l o w r e l a t i v e h u m i d i t i e s b e t w e e n 2 0 ¾ a n d 3 0 ¾ c e n t e r e d n e
a r 5 6 K m a l t i t u d e . T h e p r o f i l e s s h o w n f o r t h e re)atlve h u m i d i t i e s a n d o t h e r p r o f i l e s
f o r C O a n d a r e a v e r a g e v e r t i c a l p r o f i l e s f o r a l l m e a s u r e m e n t s d u r i n g 1 9 8 0 in t h e cer_
r a d o a n d in t h e t r o p i c a l f o r e s t r e g i o n s o f B r a z i l . I n d i v i d u a l p r o f i l e s ( D e l a n y e t a l . ,
1 9 8 5 ) s h o w e d s h a r p e r d i s c o n t i n u i t i e s b e t w e e n t h e b o u n d a r y l a y e r a n d t h e f r e e t r o p o s p h e r e .
P l o t t e d in F i g u r e s 1 2 2 0 is a l s o t h e s p r e a d , e x p r e s s e d in o n e s t a n d a r d d e v i a t i o n , as
t h e d o t t e d c u r v e o n t h e r i g h t h a n d s i d e o f t h e a v e r a g e p r o f i l e s . T h e p o t e n t i a l t e m p e r a
t u r e p r o f i l e s f o r b o t h r e g i o n s a r e s h o w n in F i g u r e s 1½ a n d 1 5 . T h e s e v a r y o n l y s l i g h t
ly w i t h a l t i t u d e in t h e b o u n d a r y l a y e r o f t h e c e r r a d o r e g i o n , i n d i c a t i n g s t r o n g n o n
-c o n v e -c t i v e , t h e r m a l m i x i n g . T h e a v e r a g e p o t e n t i a l t e m p e r a t u r e p r o f i l e o v e r t h e t r o p i
c a l f o r e s t s s u g g e s t s t h e r e s i d u a l e f f e c t s o f m o i s t a d i a b a t i c m i x i n g r e l a t e d t o c o n v e c t i
v e a c t i v i t y o r a d v e c t i o n o f a i r f r o m r e g i o n s w i t h c o n v e c t i v e a c t i v i t y .
In o r d e r t o s e p a r a t e c l e a r l y t h e a i r m a s s e s , w h i c h a r e p o l l u t e d b y b i o m a s s
b u r n i n g , f r o m c l e a n a i r , e x t e n s i v e t r a j e c t o r y a n a l y s e s w e r e p e r f o m e d f o r t h e f l i g h t
p r o g r a m , a d o p t i n g t h e i s e n t r o p i c p a c k a g e o f H a a g e n s o n & S h a p i r o ( 1 9 7 9 ) . T h e t r a j e c t o
r i e s w h i c h w e r e s o d e r i v e d a r e s h o w n in F i g u r e 1 6 . T h e p r o f i l e s in u n p o l l u t e d air
m a s s e s a r e m a i n l y l o c a t e d b e t w e e n t h e l a t i t u d e s 2. 1 - 6 . 2 ° $ , w h i l e t h e p r o f i l e s b e t w e e n
9 . 2- l 6 . 6 ° S w e r e c l e a r l y a f f e c t e d b y b u r n i n g a c t i v i t i e s in t h e b o u n d a r y l a y e r . B e t w e e n
included in the p r e s e n t a n a l y s i s . T h e a v e r a g e o z o n e a n d c a r b o n m o n o x i d e vertical profJ_ les f o r b o t h r e g i o n s a r e shown in F i g u r e s 1 7 2 0 . C l e a r l y t h e m o s t r e m a r k a b l e f e a t u r e s are t h e m u c h l a r g e r , m e a s u r e d o z o n e c o n c e n t r a t i o n s In t h e lowest 3. 5 K m in t h e c e r r a d o
regions a n d t h e d r a s t i c d e c r e a s e o f CO m i x i n g ratios a b o v e t h e b o u n d a r y layer in b o t h tropical r e g i m e s . In c o m p a r i n g t h e m e a s u r e d c o n c e n t r a t i o n s o v e r Brazil w i t h d a t a o b s e r v e d o v e r t h e P a c i f i c o n G A M E N T A G in A u g u s t 1977 (Routhier e t a l , , 19S0) a n d a l o n g the w e s t c o a s t o f S o u t h A m e r i c a in A u g u s t 197** (Seiler a F o s h a m , 19Sl) a t t h e same lati tudes a t 5-6.5 K m a l t i t u d e , w e n o t i c e a l m o s t t w o times h i g h e r o z o n e v o l u m e mixing rat_i_ os in t h e f r e e t r o p o s p h e r e a b o v e B r a z i l . F r o m a b o u t k t o 7 K m o u r m e a s u r e m e n t s o v e r both r e g i o n s o f Brazil s h o w v o l u m e m i x i n g r a t i o s o f a b o u t ^050 p p b v (see F i g u r e s 17
and 1 8 ) . O u r m e a s u r e d o z o n e c o n c e n t r a t i o n s j u s t a b o v e t h e tropical forest c a n o p y d e crease to a b o u t 20 p p b v , b u t t h e a v e r a g e v a l u e in t h e b o u n d a r y layer is a b o u t 30 p p b v , which is s l i g h t l y h i g h e r than t h e 20 ppbv m e a s u r e d d u r i n g t h e G A M E T A G f l i g h t s in 1977 (Routhier e t a l. , 1980) . S e i l e r â F i s h m a n ( I 9 8 I ) r e p o r t e d v a l u e s o f o n l y 10 p p b v . T h e m e a s u r e d o z o n e c o n c e n t r a t i o n s in t h e b o u n d a r y layer o v e r t h e c e r r a d o o f a b o u t 55 ppbv
is, h o w e v e r , m u c h h i g h e r than o v e r t h e P a c i f i c a n d a l s o o v e r t h e f o r e s t r e g i o n s . C l e a r l y , o z o n e is p r o d u c e d here b y p h o t o c h e m i c a l r e a c t i o n s .
T h e m e a s u r e d C O c o n c e n t r a t i o n in t h e b o u n d a r y layer o f b o t h regions o f Brazil are v e r y h i g h c o m p a r e d t o typical o b s e r v a t i o n s in m a r i n e o r near coastal a r e a s w i t h values in t h e 5 0 - 1 0 0 p p b v range ( S e i l e r , 1971!; Heidt e t a l. , 1 9 8 0 ; Seiler a F i s h m a n , I 9 8 I ) . In t h e b o u n d a r y layer o f t h e tropical f o r e s t s m e a s u r e d CO c o n c e n t r a t i o n s avera_ ge a b o u t 3 0 0 ppvb (Figure 1 9 ) . C a r b o n m o n o x i d e m i x i n g ratios w e r e e v e n higher Iti the c e r r a d o b o u n d a r y layer a n d v e r y v a r i a b l e (Figure 2 0 ) . M e a s u r e d concent rat ions w e r e higher t h a n in rural a r e a s a t m i d - l a t i t u d e s In t h e n o r t h e r n h e m i s p h e r e . In f a c t , the b o u n d a r y layer v a l u e s shown f o r t h e c e r r a d o region in F i g u r e 2 0 a r e u n d e r e s t i m a t i -o n s , b e c a u s e CO c -o n c e n t r a t i -o n s larger than ^00 ppbv c -o u l d n -o t b e m e a s u r e d b e c a u s e -o f
recorder s e t t i n g l i m i t a t i o n s .
A b o v e t h e b o u n d a r y layer t h e m e a s u r e d C O c o n c e n t r a t i o n s a r e likewise s u b s t a n t i a ^ ly h i g h e r than those m e a s u r e d o v e r t h e o c e n a s a t s i m i l a r latitudes a n d times o f t h e year. T h e s t u d i e s b y Heidt e t a l . ( I 9 8 D ) , Seiler (1971») a n d Seiler & F i s h m a n (Τ 981 )
indicate v o l u m e m i x i n g r a t i o s o f 5 0 1 5 0 p p b v in t h e m a r i n e , free t r o p o s p h e r e . O u r
o b s e r v a t i o n s a b o v e k K m a l t i t u d e s a g r e e t h e s e v a l u e s . H o w e v e r , t h e y show m u c h h i g h e r
CO v o l u m e m i x i n g r a t i o s b e t w e e n t h e t o p o f t h e b o u n d a r y l a y e r a n d k K m (600 m b ) . This
is p a r t l y d u e t o t h e a v e r a g i n g o f several individual p r o f i l e s , b u t a l s o indicates
upward t r a n s p o r t f r o m t h e b o u n d a r y l a y e r .
D I S C U S S I O N
R E S U L T S O B T A I N E D F R O M F I R E S A M P L I N G
T h e c a n s a m p l e d a t a c o l l e c t e d d u r i n g t h e 1 9 7 9 a n d I98O e x p e r i m e n t s a n d p r e s e n t e d
in T a b l e 1 i n d i c a t e that t h e g e o m e t r i c m e a n o f t h e e m i s s i o n r a t i o s o f C O a n d C H ^ c o m p a
red to C 02 f r o m tropical b i o m a s s b u r n i n g a r e c l o s e to )2% a n d 0.9¾ w i t h u n c e r t a i n t i e s of f a c t o r s of 2 a n d 2 . 5 , r e s p e c t i v e l y . T h e a r i t h m e t i c m e a n s a r e 15.1
»¾ a n d 1.2¾ respec tively w i t h s t a n d a r d d e v i a t i o n s o f 10¾ a n d 1¾. T h e p l u m e f l i g h t r a t i o s a r e 1^.5¾ for CO a n d 1.7¾ f o r C H ^ , T h e s e r a t i o s a g r e e c l o s e l y w i t h t h o s e d e r i v e d by us for fires in t e m p e r a t e f o r e s t s a n d g r a s s l a n d s , \h% a n d 1.6¾ r e s p e c t i v e l y (Crutzen e t a l . , 1979) W e m a y , t h e r e f o r e , a d o p t v a l u e s of a b o u t 13¾ for C O a n d 1.¾¾ for C H ^ a s t h e a v e r a g e
ratios to u s e for d i s c u s s i o n s o n t h e global e m i s s i o n rates o f CO a n d C H ^ to t h e a t m o s -p h e r e . A s d o n e in t h e e a r l i e r study w e c a n t h e n d e r i v e t h e global -p r o d u c t i o n rates of CO a n d C H ^ a n d o t h e r s p e c i e s by m u l t i p l i n g t h e s e r a t i o s w i t h t h e e s t i m a t e d global p r o -d u c t i o n of C 02 by b i o m a s s b u r n i n g o f
2.2-1» χ 101 5g C p e r y e a r m o s t l y 'in the t r o p i c s (Seiler & C r u t z e n , 1 9 8 0 ) . T h e d e r i v e d n u m b e r s w h i c h f o l l o w n e x t r e m a i n , h o w e v e r ,
u n c e r t a i n b y a t least a f a c t o r o f t h r e e .
B i o m a s s b u r n i n g c a n lead to a n annual r e l e a s e o f lo'^g CO to t h e a t m o s p h e r e , w h i c h s h o u l d be c o m p a r e d to t h e input o f 6 χ lo'^g CO by industrial a c t i v i t i e s ( S e i l e r ,
197*0. T h e c a l c u l a t e d a v e r a g e e m i s s i o n rate o f m e t h a n e is 6 χ 1 D1^ g C H ^ o r k.$ χ 10.'^ g C per y e a r . T h i s i m p l i e s c l e a r l y a s i g n i f i c a n t c o n t i b u t i o n to t h e a t m o s p h e r i c C H ^ b u d g e t , a s it is c u r r e n t l y e s t i m a t e d t h a t a b o u t 31* x Jβ g C H ^ a r e b r o k e n d o w n in
t h e a t m o s p h e r e b y r e a c t i o n w i t h t h e O H r a d i c a l , a d o p t i n g a n a v e r a g e O H c o n c e n t r a t i o n
in t h e a t m o s p h e r e o f a b o u t 6 χ 1 m o l e c u l e s / c m " * ( C r u t z e n & Gidel , 1 9 8 3 ; Vol ζ e t a l . , I98I ; C r u t z e n , 1983). Total e m i s s i o n s o f n o n m e t h a n e h y d r o c a r b o n s a r e c a l c u l a t e d to
r e a c h 3.Ί χ 1 0 ^ g C / y e a r , a b o u t e q u a l t o t h e m e t h a n e e m i s s i o n s . T h e o x i d a t i o n of
all h y d r o c a r b o n s w h i c h a r e p r o d u c e d b y b i o m a s s b u r n i n g h a s , t h e r e f o r e , t h e p o t e n t i a l i t
to p r o d u c e 2 χ 10 g CO a n n u a l l y in t h e t r o p o s p h e r e , w h i c h is a b o u t 2 5 ¾ o f t h e d i r e c t p r o d u c t i o n o f CO by f i r e s . T h e m o s t p r o m i n a n t g r o u p o f g a s e s e m i t t e d a m o n g t h e n o n - m e t h a n e h y d r o c a r b o n s a r e t h e r e a c t i v e a l k e n e s (-^5¾) w i t h e t h y l e n e b e i n g m o s t a b u n d a n t . T h r o u g h these e m i s s i o n s t h e r e is t h e p o s s i b i l i t y o f s i g n i f i c a n t o x i d a n t (ozo ne) f o r m a t i o n . W e will r e t u r n to a d i s c u s s i o n o f this issue w h e n w e d i s c u s s t h e o z o n e o b s e r v a t i o n s . T h e n e x t m o s t a b u n d a n t c l a s s o f h y d r o c a r b o n s e m i t t e d by t h e f i r e s a r e the a l k a n e s , e s p e c i a l l y e t h a n e a n d p r o p a n e . T h e c o m p o s i t i o n o f t h e n o n - m e t h a n e h y d r o c a r b o n s p r o d u c e d by t h e f i r e s is s h o w n in T a b l e 1.
The g e o m e t r i c m e a n o f t h e e m i s s i o n rate r a t i o s o b t a i n e d for C O S is a b o u t k.~l χ 1 0 " ^ , a n d t h e a r i t h m e t i c m e a n is 8.2 χ 10 ., T h e s e r a t i o s a r e t w o t o t h r e e t i m e s
1ower than t h e e a r l i e r deri v e d a v e r a g e r a t i o o f 1.6 χ 10 ^ ( C r u t z e n e t a l. , 1979) , b u t t h e u n c e r t a i n t y in this r a t i o is v e r y l a r g e . A d o p t i n g 6.5 χ 10 ^ a s the a v e r a g e n u m
b e r , w e c a n d e r i v e a global s o u r c e o f C O S f r o m b i o m a s s b u r n i n g o f 7 χ 10 g S a n n u a l l y
F o r t u i t o u s l y , this p r o d u c t i o n is equal t o t h e s t r a t o s p h e r i c loss o f C O S b y p h o t o l y s i s in u l t r a v i o l e t s u n l i g h t ( C r u t z e n 1 9 7 6 ; T u r c o e t a l ., 1980). J o h n s o n (1981) has
p o s t u l a t e d t h a t t h e o c e a n s u r f a c e w a t e r s c o u l d r e m o v e a b o u t 2 χ lo''g S o f C O S a n n u a l l y by d i s s o l u t i o n a n d h y d r o l y s i s , l e a d i n g t o t h e f o r m a t i o n o f a n d C O ^ , O n t h e o t h e r
h a n d , R a s m u s s e n e t a l. (1982) f o u n d s e a w a t e r a 1 w a y s t o b e s u p e r s a t u r a t e d w i t h r e g a r d
f r o m t h e o c e a n s to the a t m o s p h e r e o f Ί χ 10 g S. In a d d i t i o n , t h e o x i d a t i o n o f C S 2 by r e a c t i o n w i t h O H h a s b e e n s h o w n b y J o n e s et a l . (1983) a n d N i k e (personal c o m m u n i c a tion) t o p r o c e e d r e a d i l y in a i r w i t h a r e a c t ion c o e f f i c i e n t o f 2 x 1 0 c m m o l e c u l e s , l e a d i n g t o t h e f o r m a t i o n o f o n e C O S a n d o n e 5 02 m o l e c u l e . T h e global industrial r e l e a s e o f C S2 t o t h e a t m o s p h e r e is a b o u t h χ 1 01 1g C S2 a n n u a l l y (Peyton e t a l. , 1 9 7 6 ) , so that t h e a t m o s p h e r i c o x i d a t i o n of t h i s a m o u n t o f C S - In the a t m o s p h e r e m a y y i e l d C O S
11
at a rate o f 1.7 χ 10 g S per y e a r . C o m p a r e d to t h e s e h i g h input rates o f C O S t o the a t m o s p h e r e , t h e C O S p r o d u c t i o n f r o m b i o m a s s b u r n i n g m a y o n l y a c c o u n t f o r 10¾. A d d i t i o nal C O S m a y be p r o v i d e d by coal b u r n i n g a n d o t h e r industrial a c t i v i t i e s . It s e e m s that a large s i n k o f COS in the e n v i r o n m e n t has n o t b e e n i d e n t i f i e d . T h e t e r r e s t r i a l b i o s -phere is the m o s t l i k e l y p o s s i b i l i t y .
T h e n e w d e r i v e d N ^ O : C 0 ^ e m i s s i o n r a t i o rate has a g e o m e t r i c m e a n of 1.5 x Ό , w i t h an u n c e r t a i n t y o f a b o u t a f a c t o r o f 3, t h e central v a l u e b e i n g r o u g h l y a f a c t o r of ten s m a l l e r t h a n t h e e a r l i e r e s t i m a t e o f 2.2 χ 10 ( C r u t z e n et a l . , 1979)- T h e
A
a r i t h m e t i c r a t i o is a b o u t two t i m e s h i g h e r . A d o p t i n g a v a l u e o f 2.5 x 10 for this 12 r a t i o , t h e global H^O p r o d u c t i o n f r o m b i o m a s s b u r n i n g c a n b e e s t i m a t e d a t 2 χ 10 g Ν per y e a r w i t h an u n c e r t a i n t y o f m o r e than a f a c t o r o f 3. T h i s v a l u e is s i g n i f i c a n t as an a n t h r o p o g e n i c s o u r c e in c o m p a r i s o n w i t h t h e e s t i m a t e d p r o d u c t i o n 1.6 χ 10 g Ν f r o m coal a n d fuel oil b u r n i n g (Weiss & C r a i g , 1 9 7 6 ) . T h e loss o f H^O in t h e s t r a t o s p h e r e
is in the range 6-11 χ 1 01 2g Ν p e r y e a r , so t h a t b i o m a s s b u r n i n g c a n a d d a signlfi -cant f r a c t i o n o f t h e total H^Q i n p u t in t h e a t m o s p h e r e . S t r a t o s p h e r i c r e a c t i o n s p r o v i de p r o b a b l y t h e o n l y loss o f a t m o s p h e r i c N ^ O . T h e r e m a i n i n g a t m o s p h e r i c e m i s s i o n s o f H^0 a r e p r o b a b l y d u e to d e n i t r i f i c a t i o n a n d n i t r i f i c a t i o n p r o c e s s e s in t h e s o i l s a n d w a t e r s ( W e i s s , 1 9 8 1 , S e i l e r , 1 9 81 ; E l k i n s e t a l . , 1 9 7 8 ; B r e m n e r e t a l . , 1 9 8 1 ) . The global b u r d e n o f a t m o s p h e r i c N^O is i n c r e a s i n g b y a b o u t 0.2¾ p e r y e a r ( W e i s s , 1981)
A n i n t e r c o r r e l a t i o n o f C O a n d N O X c o n c e n t r a t i o n s f r o m f l i g h t s 10 — 13 w a s m a d e to d e t e r m i n e t h e C 0 / N O X e m i s s i o n f r o m t h e large s c a l e b r u s h f i r e s in the c e r r a d o . D u r i n g the p o r t i o n s o f t h e 198O f l i g h t s in t h e c e r r a d o b o u n d a r y l a y e r , the a i r c r a f t s p e c i f J c a £ ly a v o i d e d s m o k e p l u m e s a n d so the r a t i o s o b t a i n e d r e l a t e to a g e d rather than f r e s h fire e m i s s i o n .
T h e r e s u l t s o f a least s q u a r e s fit f o r t h e CO v e r s u s NOX d a t a was 73 - k for the r a t i o o f C O / N O X in t h e b o u n d a r y layer o v e r the c e r r a d o a n d m a y be t a k e n to be t h e e m i s sion ratio f o r t h e large s c a l e f i r e s . G i v e n that a f a i r l y c o n s t a n t v a l u e o f 0.1k -0.02 for t h e C O / C O ^ r a t i o h a s b e e n d e t e r m i n e d for all f i r e e v i s s i o n s m e a s u r e d in this s t u d y , a v a l u e of
C O , CO CO i * x
— L
= 5 3 5 + 9 5 N O X N O X CO may be o b t a i n e d .& M c M a h o n , 1 9 8 0 ) . T e s t s on NO e m i s s i o n s f r o m w o o d b u r n i n g f i r e p l a c e s indicate v a l u e s o f 2000 ( M u h l b a i e r - D a s c h , Τ 9 8 2 ) a n d 710 ( D e A n g e l i s e t a l . , 1 9 8 0 ) . W e b e l i e v e that o u r m e a s u r e m e n t s p r e s e n t an u n d e r e s t i m a t e of the NOX p r o d u c t i o n in o p e n v e g e t a t i o n fi -r e s , b e c a u s e all o u -r s i m u l t a n e o u s in s i t u m e a s u -r e m e n t s o f NOX a n d CO w e -r e m a d e o u t s i d e fire p l u m e s so that w e m a y s u s p e c t that s o m e N O X m a y h a v e b e e n r e m o v e d by p h o t o c h e m i c a l r e a c t i o n s a n d dry d e p o s i t i o n .
T h e d e t e r m i n a t i o n of the NOX to C 0 „ rat io of ^ 2 χ 1 0 " ^ i n d i c a t e s the p o s s i b i1 i ty 1 2
o f an NOX p r o d u c t i o n o f 7 x 10 g Ν per year f r o m b i o m a s s b u r n i n g a c t i v i t i e s in the t r o p i c s . T h i s c o m p a r e s to an industrial s o u r c e o f 20 χ 1 01 g N / y e a r (Crutzen e t al ., 1979) a n d a l i g h t n i n g s o u r c e o f a b o u t 3 x íft | N / Y e a r w i t h an u n c e r t a i n t y o f a f a c t o r o f t h r e e ( C r u t z e n , 1 9 8 3 ) . C o n s e q u e n t l y , the NOX e m i s s i o n s f r o m b i o m a s s b u r n i n g r e p r e s e n t a n i m p o r t a n t souce o f n i t r o g e n o x i d e s to the tropical a t m o s p h e r e w i t h a strong potential for an impact on the p h o t o c h e m i s t r y o f the t r o p i c a l , c o n t i n e n t a l a r e a s .
O u r m e a s u r e m e n t s in Brazil h a v e , t h e r e f o r e , c o n f i r m e d that a g r i c u l t u r a l bur -n i -n g a c t i v i t i e s ca-n put s u b s t a -n t i a l q u a -n t i t i e s o f C O , C H ^ , -n o -n - m e t h a -n e h y d r o c a r b o -n s , NOX and N O into the a t m o s p h e r e a n d that t h e s e a c t i v i t i e s may v e r y well be as i m p o r t a n t to global a i r c h e m i s t r y as the industrial a c t i v i t i e s in the d e v e l o p e d w o r l d . H o w e v e r , e s p e c i a l l y for N O X , N^O (and COS) t h e v a r i a b i l i t y in m e a s u r e d e m i s s i o n rate r a t i o s a r e so large that there remain large u n c e r t a i n t i e s in the q u a n t i f i c a t i o n s o f t h e e m i s s i o n
ra t e s .
A I R C R A F T F L I G H T R E S U L T S - P R O F I L E S O F O Z O N E A N D C A R B O N M O N O X I D E
T h e m o s t i n t e r e s t i n g o b s e r v a t i o n s w h i c h w e m a d e c o n c e r n the m e a s u r e d p r o f i l e s o f o z o n e (Figures 17 and 18) a n d c a r b o n m o n o x i d e ( F i g u r e s 19 and 2 0 ) . T h e y c l e a r l y p o i n t to a s u b s t a n t i a l p r o d u c t i o n o f c a r b o n m o n o x i d e in t h e b o u n d a r y l a y e r s o f b o t h t h e c e r -rado a n d s e l v a r e g i o n s , w h i l e o z o n e is c l e a r l y p r o d u c e d in t h e c e r r a d o , b u t d e s t r o y e d in t h e s e l v a .
T h e p r o d u c t i o n o f c a r b o n m o n o x i d e a b o v e the f o r e s t s c a n b e e x p l a i n e d by t h e rapid o x i d a t i o n o f r e a c t i v e h y d r o c a r b o n s e m i t t e d by f o l i a g e in a c c o r d a n c e w i t h the p r o posal by Z i m m e r m a n e t a l. ( 1 9 7 8 ) . T h i s can b e s h o w n by a s i m p l e c a l c u l a t i o n of the e q u i l i b r i u m v o l u m e m i x i n g ratios o f CO w i t h the a v e r a g e m e a s u r e d I s o p r e n e (C^Hg) concen_ t r a t i o n s o f a b o u t 1.7 x 10 ^ (1.7 ppbv) in the f i r s t 350 m a b o v e t h e f o r e s t c a n o p y du -ring o n e o f o u r f l i g h t s , a s s u m i n g t h a t the r e a c t i o n s w i t h h y d r o x y l (OH) a r e i m p o r t a n t , so that
R21 C_Hg + O H -+ C Η + H20 f u r t h e r t*C0 ( Z i m m e r m a n et al . , 1978) Rl CO + O H -*⊅ H + CO r e a c t i o n s
equal to 2 χ 10 , w h i c h is m u c h l a r g e r t h a n w e o b s e r v e d . T h i s s h o w s c l e a r l y that t h e o x i d a t i o n o f i s o p r e n e a n d o t h e r h y d r o c a r b o n m a y v e r y well b e r e s p o n s i b l e for the h i g h c a r b o n m o n o x i d e c o n c e n t r a t i o n s in t h e b o u n d a r y layer a b o v e the f o r e s t s . In r e a l i t y w e m u s t c o n s i d e r that the y i e l d o f CO f r o m C^Hg o x i d a t i o n m a y n o t b e equal to Ί , that the m e a s u r e d c o n c e n t r a t i o n s of 1.7 ppbv o f c^ H g m a y not b e c h a r a c t e r i s t i c for t h e b o u n d a r y layer a n d that h y d r o x y l c o n c e n t r a t i o n m a y be so low o v e r t h e tropical f o r e s t s , that o t h e r c h e m i c a l r e a c t i o n s m a y play a r o l e in the i n i t i a t i o n o f the isoprene o x i d a -t i o n , e . g . -the r e a c -t i o n w i -t h o z o n e . L i k e w i s e , -the lack o f k n o w l e d g e o f -the r e a c -t i o n m e c h a n i s m s w h i c h lead to the o x i d a t i o n o f h y d r o c a r b o n s in the a t m o s p h e r e , e s p e c i a l l y in the a b s e n c e o f N O , has b e e n r e c o g n i z e d ( e . g . , Z i m m e r m a n e t a l. , 1978) a n d it w a s p o i n t e d o u t that m a n y o x y g e n a t e d s p e c i e s m a y b e f o r m e d w h i c h can be r e m o v e d from the a t m o s p h e r e b y r a i n f a l l o r u p t a k e by v e g e t a t i o n . H o w e v e r , a l t h o u g h it is clear that h y d r o c a r b o n o x i d a t i o n m a y v e r y w e l t b e the s o u r c e o f b o u n d a r y layer CO in the f o r e s t e d r e g i o n s , w i t h o u t f u r t h e r m e a s u r e m e n t s , w e c a n n o t w i t h c e r t a i n t y d i s c o u n t the p o s s i b i lity that c a r b o n m o n o x i d e is d i r e c t l y e m i t t e d by the f o r e s t s in m u c h larger rates than found by S e i l e r & Giehl (1977) for t e m p e r a t e v e g e t a t i o n , T h e l i m i t e d a m o u n t o f d a t a a v a i l a b l e to us is not a d e q u a t e to i d e n t i f y w i t h c e r t a i n t y the s o u r c e o f c a r b o n monox_j_ de o v e r the tropical f o r e s t a r e a s . In a d d i t i o n to C^Hg o t h e r h y d r o c a r b o n s are e m i t t e d by t h e f o r e s t s w h i c h m a y l i k e w i s e b e c o n v e r t e d to CO by p h o t o c h e m i c a l r e a c t i o n s ( see T a b l e 3) .
tt is c l e a r that t h e h i g h c o n c e n t r a t i o n s o f CO in t h e c e r r a d o b o u n d a r y layer d u ring the d r y s e a s o n (see f i g u r e 20) a r e c a u s e d by t h e m a n y f i r e s in this region at that t i m e o f t h e y e a r . B e c a u s e of large e m i s s i o n s o f s m o k e , v i s i b i l i t y is o f t e n p o o r .
W i t h the f e w a v a i l a b l e d a t a o n i s o p r e n e c o n c e n t r a t i o n s d u r i n g d a y t i m e a b o v e the tropical f o r e s t , w e m a y try to m a k e a r o u g h e s t i m a t e o f t h e loss o f o z o n e t h r o u g h r e a c t i o n s w i t h C^Hg by t r o p i c a l f o r e s t s . T h e r a t e c o e f f i c i e n t for the r e a c t i o n
C - Hs * p r o d u c t s h a s r e c e n t l y b e e n d e t e r m i n e d by A d e n i j i et a l . (1981) a n d for t r o p i c a ! -17 3 -1
c o n d i t i o n s w e m a y u s e as the v a l u e 2 x 1 0 c m m o l e c u l e . W j t h a v e r a g e v o l u m e m i x i n g r a t i o s o f 30 p p b v in the b o u n d a r y layer w e c a l c u l a t e that t h e m e a n l i f e t i m e o f
isoprene a g a i n s t r e a c t i o n w i t h o z o n e is a b o u t 2k h r s . If r e a c t i o n w i t h o z o n e w e r e the only s i n k f o r C ^ H g , the l i f e t i m e o f t h i s g a s in the a t m o s p h e r e w o u l d be long e n o u g h to a l l o w t h o r o u g h m i x i n g t h r o u g h the m i x e d l a y e r , so that the loss o f o2one can be
11 - 2 - 1
c a l c u l a t e d to 10 m o l e c u l e s c m s d u r i n g d a y t i m e . It s h o u l d be a d d e d , h o w e v e r , that o z o n e d o e s a l s o r e a c t w i t h t e r p e n e s a n d C g C ^ a l k e n e s , w h i c h a r e l i k e w i s e a b u n -dant a c c o r d i n g to the o b s e r v a t i o n s listed in T a b l e 3- F u r t h e r m o r e , o z o n e is d e s t r o y e d by r e a c t i o n s w i t h h y d r o c a r b o n f r a g m e n t s a n d w i t h h y d r o p e r o x y l (HO^) a n d by the t w o reac_ t ions
R2 0 + hv 4 0 {1D ) + 02 (λ< 310 nm)
